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Title: Femtosecond-resolved semiconductor dynamics with mid- and far-infrared pulsed lasers
Author: Nikzad, Lida
ISNI:       0000 0004 2679 0047
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2007
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In this thesis mid-infrared time-resolved pump-probe measurements are presented to evaluate spin dynamics in narrow gap semiconductors. The polarization of the pump beam is modulated and the transmittance change in the probe beam is measured. The optical polarization is measured versus time delay and its decay yields the spin lifetime. Results show that the spin lifetime decreases with increasing temperature. Between InAs and Insb films, although InAs shows longer spin lifetime, it has an accumulation layer in the surface with high current and very short spin lifetime, while InSb has a surface depletion layer. The spin dephasing dominates for the range of temperature 77 - 293 K for thick films, however thin films show stronger spin flip relaxation mechanism. For AlInSb/InSb quantum wells, the spin lifetime depends on the well width, mobility, and carrier concentration, and the dephasing mechanism dominates for high mobility, but for low mobility at low temperature the spin flip scattering is dominant. We have also investigated the Lande g-factor for the first time at room temperature, using the same technique by adding an external magnetic field causing spin precession. Our experimental results show that with increasing temperature and energy, the absolute g-factor, decreases. In comparison, simple predictions of k.p theory for temperature dependency of g-factor, which changes primarily because of the change in the band gap, suggest the opposite. We find leaving only the dilational part in the temperature dependence of the energy gap, improves the consistency between experimental and theoretical g-factors. Finally, a far-infrared time-resolved pump-probe study of population dynamics of shallow donor impurity states (P, As) in silicon shows that at low temperatures, the dominant linewidth broadening is due to direct phonon decay rather than dephasing collisions or inhomogeneous broadening. The achieved long lifetimes are convenient for applications such as quantum information processing.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available